Certain conventional vehicle wheel alignment systems use alignment elements referred to as “alignment heads” that are attached to the wheels of a vehicle to measure various angles of the wheels and suspension. These angles are communicated to a host computer system, where they are used in the calculation of vehicle alignment angles. In a standard conventional aligner configuration, four alignment heads are attached to respective wheels of a vehicle. Each alignment head comprises two horizontal or toe measurement sensors and two vertical or camber/pitch sensors. Each alignment head also contains electronics to support overall sensor data acquisition as well as communications with the aligner console, local user input, and local display for status feedback, diagnostics and calibration support. Other conventional alignment systems, referred to as “visual aligners,” use optical targets attached to each vehicle wheel instead of sensors. The targets are imaged by cameras, and these visual images are used to calculate the vehicle wheel alignment angles.
Such alignment equipment usually includes a wheel clamp that attaches to a vehicle's wheel and carries the alignment element (i.e., the sensor equipment that measures the alignment angles, or the optical target). Referring now to FIG. 1, a conventional wheel clamp 100, such as described in U.S. Pat. No. 7,870,677, includes a pair of upper and lower sliding brackets 105, 110, respectively, for engaging the rim of the vehicle wheel, and a center bracket 115 for holding an alignment element, such as an optical target or an alignment head. Brackets 105, 110, 155 are all slidably mounted on a pair of guide bars 120, 125. A lead screw 130 threadingly engages upper and lower brackets 105, 110 for clamping the clamp 100 to the vehicle wheel. The vehicle being aligned is usually positioned on a vehicle alignment lift at heights from three to four feet for performing alignments. The vehicle can be raised even higher, up to six feet, for servicing the vehicle from underneath.
Attachment of the wheel clamp to the vehicle wheel is typically accomplished using a set of three or more gripping devices or grabbers which are part of the wheel clamp. The grabbers wedge thin metal fingers in the annular groove between the tire and the wheel rim at several locations around the wheel circumference. The grip is tightened by means of a screw thread driver or similar means that pulls the grabbers toward the wheel center. In an alternative methodology, used particularly on steel wheels, the grabbers are removed and the grabber supports are located against the inner surface of the steel wheel. The grabber supports are driven outward from the wheel center until they lock the wheel clamp in place. Either method requires metal to metal contact between the wheel clamp and the vehicle wheel rim, so some damage to the surface of the wheel is inevitable.
Speed of attachment is another critical aspect of wheel clamp functionality. Aligning the metal fingers of conventional wheel clamps into the small annular space between the wheel rim and tire is a challenge that requires precise placement. Once the grabbers are positioned properly, care must be taken to prevent one or more grabbers from popping out as the clamp is tightened. This process takes considerable time and care to prevent unnecessary damage to the rim surface.
Since tires and rims come in a wide variety of sizes, it is useful to have a single wheel clamp that will address the extremities of the size range without the need for additional, nonintegral adaptors or extensions.
Other wheel clamp designs that attempt to solve rim damage problems exist. For example, the Beissbarth Magnetic Wheel Lug Clamp attempts to mitigate rim damage by using adjustable magnets placed in contact with vehicle wheel lug nuts as a means of securing the wheel clamp in place. Since many vehicles have lug nuts covered by a cosmetic wheel cover or hub cap, the need to remove the wheel cover is a distinct disadvantage. In addition, the adjustment required to various lug nut patterns can be tedious and slow. A recent design described in U.S. Patent Application Publication 2011/0001821 incorporates a method of gripping the tire tread with two cam operated arms while pressing a plastic annular ring against the rim surface for support. This design does not self center, and still has a potential for rim surface damage. Moreover, multiple, nonintegral arms are needed to allow functionality with all possible rim diameters.
Therefore, a need exists for a wheel clamp that does not touch any part of the vehicle wheel surface, provides secure mounting with an emphasis on speed and ease of use, covers a wide range of wheel diameters without the need for additional nonintegral apparatus, and centers automatically on the vehicle wheel centerline as the clamp is tightened.